001  
FXCA20 KWBC 011854  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
154 PM EST THU FEB 01 2018  
 
TROPICAL DISCUSSION FROM FEB 01/12 UTC: A 500 HPA HIGH HAS  
ESTABLISHED OVER SOUTHERN PORTIONS OF THE YUCATAN PENINSULA...AND  
IS ANCHORING A MID-LEVEL RIDGE THAT COVERS MOST OF THE CARIBBEAN.  
THE MOST PREDOMINANT RIDGE AXIS EXTENDS EAST INTO THE LESSER  
ANTILLES. THIS IS SUSTAINING A STRONG SUBSIDENCE CAP ALONG THE  
NORTHERN CARIBBEAN...BUT ALSO SIGNIFICANT DRYING ABOVE THE  
INVERSION. A VERY SHALLOW PLUME OF MOISTURE IS FORECAST TO ENTER  
THE NORTHEASTERN CARIBBEAN ON FRIDAY. THIS WILL SUSTAIN AN  
ENHANCEMENT IN TRADE WIND SHOWERS TO SUSTAIN ACCUMULATION OF  
05-10MM/DAY AND MAXIMA OF 15MM IN PUERTO RICO AND THE VIRGIN  
ISLANDS. THIS WILL EXTEND INTO SUNDAY WHILE WEAKENING.  
OTHERWISE...CONVECTION WILL BE VERY ISOLATED THROUGH THE CYCLE  
WHILE PRODUCING TRACE RAINFALL AMOUNTS. AS THE WEEKEND  
PROGRESSES...UNDER THE INFLUENCE OF PERSISTENT NORTHERLY WINDS AT  
MID-LEVELS...EXPECTING A SLIGHT COOLING OF MID-LEVEL TEMPERATURES  
IN THE EASTERN CARIBBEAN. THIS WILL LEAD TO A GRADUAL  
DESTABILIZATION OF THE LOWER TROPOSPHERE...AND CONSEQUENT  
WEAKENING OF THE CAP. THE RESULT WILL BE AN INCREASE IN THE DEPTH  
OF TRADE WIND CUMULUS...AND ASSOCIATED INCREASE IN PRECIPITATION.  
THIS WILL BE FURTHER ENHANCED BY A TUTT-INDUCED TROUGH EMBEDDED IN  
THE TRADES...FORECAST TO ENTER THE LESSER ANTILLES DURING SUNDAY.  
 
TO THE NORTH...A MID-UPPER TROUGH IS WEAKENING WHILE MEANDERING  
INTO THE CENTRAL NORTH ATLANTIC. IN ASSOCIATION WITH THIS  
TROUGH...THE REMNANTS OF A FRONT ARE LOSING DEFINITION ACROSS THE  
SOUTHERN BAHAMAS. UNDER THE INFLUENCE OF THE MID-LEVEL RIDGE TO  
THE SOUTH AND THE CONVERGENT SIDE OF THE EXITING UPPER  
TROUGH...THE SUBSIDENCE CAP IS LOWERING IN THE REGION...AND THE  
TROPOSPHERE IS BECOMING DRIER. THIS WILL LEAD TO GENERALLY FAIR  
CONDITIONS IN THE BAHAMAS AND CUBA...ALTHOUGH REMNANT SHOWERS WILL  
BE PRESENT IN SOUTHERN PORTIONS OF THE REGION. THROUGH EARLY  
FRIDAY...ENHANCED TRADE WIND CONVERGENCE WILL STILL SUSTAIN  
SCATTERED SHOWERS IN THE SOUTHERN BAHAMAS AND PORTIONS OF THE  
CENTRAL ATLANTIC COAST OF CUBA. YET...MAXIMUM ACCUMULATIONS WILL  
LIMIT TO 10MM/DAY.  
 
A SECOND FRONT IS MEANDERING ACROSS THE CENTRAL UNITED  
STATES...AND IS FORECAST TO ENTER THE GULF OF MEXICO IN EARLY  
HOURS OF FRIDAY. BY FRIDAY EVENING THE FRONT WILL EXTEND ACROSS  
CENTRAL FLORIDA...WHILE BECOMING STATIONARY ACROSS THE CENTRAL  
GULF INTO CENTRAL TAMAULIPAS. BY SATURDAY EVENING THE BOUNDARY  
WILL REACH THE NORTHWESTERN BAHAMAS WHILE BECOMING  
STATIONARY...AND WILL EXTEND ACROSS THE FLORIDA STRAIGHT INTO THE  
CENTRAL GULF OF MEXICO. MODELS ARE SUGGESTING THE DEVELOPMENT OF  
AN ILL-DEFINED SHEAR LINE...WHICH IS FORECAST TO EXTEND INTO THE  
SOUTHEASTERN BAHAMAS AND HOLGUIN IN CUBA AND EXTREME NORTHEASTERN  
HONDURAS BY FRIDAY EVENING...AND INTO THE SOUTHEASTERN  
BAHAMAS/TURKS AND CAICOS BY SATURDAY EVENING...TO THEN LOSE  
DEFINITION. GIVEN THE PRESENCE OF DRY MID-LEVELS AND THE LACK OF  
DYNAMIC FORCING IN THE MID TROPOSPHERE...RAINFALL AMOUNTS IN  
ASSOCIATION WITH THESE SYSTEMS WILL BE LIMITED. THE LARGEST  
ACCUMULATIONS WITH THE FRONT ARE EXPECTED BY SATURDAY-SUNDAY IN  
THE NORTHWESTERN BAHAMAS...WHERE SHOWERS WILL LEAD TO 05-10MM/DAY  
AND ISOLATED MAXIMA OF 15MM. REGARDING THE SHEAR LINE...EXPECTING  
RAINFALL ACCUMULATIONS OF 00-05MM/DAY AND ISOLATED MAXIMA OF 10MM  
TO AFFECT EASTERN PORTIONS OF THE ATLANTIC COAST OF CUBA AND THE  
SOUTHEASTERN BAHAMAS ON FRIDAY-SATURDAY...THEN CONSTRAINING TO  
EASTERN PORTIONS OF CUBA ON SATURDAY-SUNDAY.  
 
ALSO IN INDIRECT ASSOCIATION WITH THE FRONT/SHEAR LINE SYSTEM...AS  
POLAR RIDGE MEANDERS EASTWARD ACROSS THE SOUTHEASTERN US...TRADES  
WILL ACQUIRE A NORTHERLY COMPONENT ONCE AGAIN IN THE GULF OF  
MEXICO/GULF OF HONDURAS ON FRIDAY THROUGH SUNDAY. THIS WILL  
DEVELOP A TRANSIENT TEHUANTEPECER JET ON FRIDAY...AND AN INCREASE  
IN MOISTURE CONVERGENCE ALONG THE NORTHERN AND NORTHEASTERN SLOPES  
OF NORTHERN CENTRAL AMERICA ON FRIDAY THROUGH SUNDAY. AS A  
RESULT...ACCUMULATIONS WILL INCREASE DURING FRIDAY. FROM  
FRIDAY-SATURDAY...EXPECTING RAINFALL ACCUMULATIONS OF 05-10MM/DAY  
AND MAXIMA OF 15-20MM DEVELOPING BETWEEN SOUTHERN VERACRUZ INTO  
NORTHEASTERN HONDURAS. ACROSS NORTHERN AND CENTRAL VERACRUZ...AND  
BELIZE/QUINTANA ROO...EXPECTING MAXIMA UNDER 10MM. BY  
SATURDAY-SUNDAY...LARGEST ACCUMULATIONS WILL CLUSTER IN CENTRAL  
GUATEMALA TO REACH 05-10MM/DAY AND MAXIMA OF 15MM...WHILE A RAPID  
DECREASING TREND IS EXPECTED IN THE REST OF THE REGION.  
 
IN THE PACIFIC...A DEEP UPPER TROUGH HAS FORMED AN UPPER LOW TO  
THE SOUTHWEST OF THE COASTS OF THE BAJA CALIFORNIA PENINSULA. AS  
THE UPPER TROUGH MEANDERS NORTHWARD WHILE WEAKENING...IT WILL  
CONTINUE VENTILATING CONVECTION OVER THE TROPICAL NORTH  
PACIFIC...MOSTLY OFF THE COASTS OF MEXICO. THIS IS PRODUCING A  
WIDESPREAD CIRRUS SHIELD...AND A FEW SHOWERS IN PORTIONS OF  
WESTERN/CENTRAL MEXICO...AND IS ENHANCING CYCLONIC VORTICITY IN  
SOUTHERN PORTIONS OF THE GULF OF CALIFORNIA/MAR DE CORTES. AS THE  
PERTURBATIONS PROPAGATE TO THE NORTHEAST...AIDED BY THE MEAN  
MID-UPPER FLOW...THEY WILL ENHANCE PRECIPITATION IN WESTERN AND  
NORTHERN MEXICO THROUGH THE CYCLE. THROUGH EARLY FRIDAY EXPECTING  
LARGEST AMOUNTS IN NAYARIT AND HIGHER ELEVATIONS OF SINALOA TO  
REACH 05-10MM/DAY AND ISOLATED MAXIMA OF 15MM. PRECIPITATION IN  
ZACATECAS/DURANGO AND NORTHERN SINALOA WILL LIMIT UNDER 10MM. BY  
FRIDAY-SATURDAY EXPECTING A PEAK IN ACCUMULATIONS ACROSS  
NORTH-CENTRAL MEXICO...FROM SOUTHEASTERN SONORA/SOUTHERN CHIHUAHUA  
AND DURANGO EAST INTO SOUTHERN COAHUILA...TO PRODUCE AMOUNTS OF  
05-10MM/DAY AND ISOLATED MAXIMA OF 15MM. ACCUMULATIONS WILL  
DECREASE AFTER.  
 
IN NORTHERN SOUTH AMERICA...FAST UPPER WESTERLIES ARE TO PERSIST  
THROUGH THE FORECAST CYCLE...AS THE SUBEQUATORIAL JET MEANDERS  
FROM THE EQUATORIAL PACIFIC ACROSS ECUADOR AND INTO VENEZUELA AND  
THE TROPICAL ATLANTIC. YET...THE MID-LEVEL FLOW OVER COLOMBIA IS  
LOSING SPEED. THIS WILL ALLOW FOR THE DEVELOPMENT OF A FEW SHOWERS  
AND THUNDERSTORMS IN THE ANDEAN REGION...PEAKING ON  
FRIDAY-SATURDAY. ACTIVITY WILL BE ALSO FAVORED BY THE ADVECTION OF  
MOISTURE FROM CONVECTION OCCURRING ALONG THE PACIFIC  
ITCZ...FORECAST TO MEANDER IN THE SOUTHERN COAST OF COLOMBIA.  
INITIALLY...EXPECTING AMOUNTS OF 05-10MM/DAY AND ISOLATED MAXIMA  
OF 15-20MM IN WESTERN COLOMBIA/VALLE DEL CAUCA/EJE CAFETERO. THIS  
IS TO INCREASE IN COVERAGE AND INTENSITY TO PRODUCE 05-10MM/DAY  
AND MAXIMA OF 15-25MM BY FRIDAY-SATURDAY. A DECREASING TREND IS  
EXPECTED ON SATURDAY...AS A DRIER AIR MASS ARRIVES FROM THE  
CARIBBEAN/VENEZUELAN LLANOS.  
 
IN THE GUIANAS...TRANSIENT WET PATTERN IS DEVELOPMENT.  
HOWEVER...ACCUMULATIONS WILL BE LIMITED BY THE PRESENCE OF  
ENHANCED VERTICAL SHEAR IN FRENCH GUIANA AND SURINAME. LARGEST  
AMOUNTS ARE EXPECTED IN EASTERN FRENCH GUIANA ON THURSDAY...WHERE  
THUNDERSTORMS WILL LEAD TO 10-15MM/DAY AND MAXIMA OF 20-45MM. WEST  
INTO SURINAME EXPECTING 05-10MM/DAY AND MAXIMA OF 15-20MM. BY  
FRIDAY-SATURDAY...ACCUMULATIONS WILL DECREASE TO 05-10MM/DAY AND  
MAXIMA OF 15MM. A FURTHER DECREASE IS EXPECTED AFTER...WHILE  
SHOWERS CONSTRAIN TO GUYANA AND EASTERN VENEZUELA TO PRODUCE  
ISOLATED MAXIMA UNDER 15MM.  
 
GORDON...NMS (BELIZE)  
NIXON...BDM (THE BAHAMAS)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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